1. Technical Field
The present invention relates generally to diffusion barriers, and more particularly, to methods for plasma enhanced atomic layer deposition of a tantalum-nitride diffusion barrier region on low-k materials that generates a sharp barrier interface.
2. Related Art
Atomic layer deposition (ALD) has been recently studied for semiconductor interconnect technology, especially for liner applications. ALD is a layer-by-layer thin film deposition technique that implements alternating exposure of chemical species. Among the various metal liners for copper (Cu) interconnect technology, tantalum-based (Ta) materials are one of the most widely used because they provide: high thermal and mechanical stability and diffusion barrier properties, and good adhesion, all of which result in good reliability. Conventional integration schemes include the deposition of a tantalum/tantalum nitride (Ta/TaN) bilayer for use as a copper (Cu) diffusion barrier by physical vapor deposition (PVD). One shortcoming of this approach, however, is that the poor conformality of the PVD technique, caused by the directional nature of the technique, has become a potential problem as device technology migrates toward a sub 100 nm regime.
Potential problems presented by ALD include contaminant incorporation and the potential reaction between precursor and substrate materials. One particular material type that exacerbates these problems is low thermal conductivity (low-k) dielectrics, such as SiLK from Dow Chemical. For example, it is generally difficult to grow tantalum-based (Ta) materials on low-k materials by conventional thermal ALD. In particular, it is difficult to grow the materials at a low enough temperature for interconnect technology, requiring growth temperature below 400° C.
In order to address the above-identified problem, plasma enhanced ALD (PE-ALD) has been suggested as an alternative approach. One possible problem of PE-ALD is the common use of atomic hydrogen (H) as a reducing agent to deposit liner materials. The use of atomic hydrogen is especially problematic for spin on low-k dielectrics. In particular, SiLK is widely known to be reactive with atomic hydrogen (H) such that etching occurs when exposed to atomic hydrogen (H). Similarly, the PE-ALD of tantalum-nitride (TaN) is known to create a reaction between metal precursors and a plasma including hydrogen.
In view of the foregoing, there is a need in the art for a technique to deposit liner material without using atomic hydrogen.